1. Field of the Invention
The present invention relates to an optical pickup. More particularly, the present invention relates to an optical pick-up for an opto-magnetic signal reproducing apparatus.
2. Description of the Related Art
FIG. 1 shows an optical pickup for an opto-magnetic disc apparatus which is disclosed in U.S. Pat. No. 5,479,387 issued on Dec. 26, 1995 in the name of Ando et al. The optical pickup 1 is composed of a plurality of optical components 2 to 10. The optical pickup 1 condenses a laser beam emitted from a laser diode 2 and reflected from a opto-magnetic disc 11, via a grating element 3, a beam splitter 4, a collimator lens 5 and an objective lens 6, to form an image on a photodetector 9 via a Wollaston prism 7 and a multi-lens 8.
However, this type of optical pickup suffers from a drawback that miniaturization of the overall apparatus is difficult. This arrangement also suffers from the drawback that improvement in reliability is difficult because a plurality of optical components must be individually assembled. This renders the arrangement unsuitable for use in compact opto-magnetic disc types of reproducing apparatus wherein a small-sized highly reliable optical pickup is vital.
FIGS. 2A and 2B show a structure disclosed in U.S. Pat. No. 4,873,429 issued on Oct. 10, 1989 in the name of Kume et al., which has been proposed for use as an optical pickup in a compact disc player arrangement. This optical pickup 21 incorporates a laser diode LD, a glass beam splitter element 23, a semiconductor substrate 24 which on which photodetectors PD1 and PD2 and the like of elements are provided. As shown, these elements are enclosed in a housing 22.
The optical pickup 21 is arranged so that an opening in the housing 22 is sealed with a transparent member 25, and so that a non-polarizing semi-transparent film 26 is provided on an inclined surface of the trapezoidally sectioned glass beam splitter element 23. An second adhesive film 27 is disposed between the beam splitter 23 and photodetector PD1 while a reflective film 28, which reflects the laser light reflected in the glass, is provided on the upper surface of the glass beam splitter element 23.
However, this optical pickup 21 cannot used for the reproduction of the opto-magnetic signals because the optical pickup 21 is a non-polarization type optical system.